LCGB Forums

Where is best to put an inline fuse on a 12 v doc variatronic, with a battery? From stator, regulator etc. Currently have just festoon, brake light and horn on the battery but will be adding more stuff soon. Got to get the basics right before I tackle that.

Put the fuse on the earth side to protect the battery itself as well as your circuits. In case the positive terminal touches metal (cable for instance).

Pete

I would put it on the positive "load" side.

petemaisey wrote:Put the fuse on the earth side to protect the battery itself as well as your circuits. In case the positive terminal touches metal (cable for instance).

Pete

+1

+2 for the earth side but thought it would get a few votes for the load side.

None of us are wrong. It's how I do it and would continue to advise and I guess that's what automobile manufacturers found to be their preferred method over the last century.

(Could run a long time this thread !)

Go belt and braces and put one on each side ?. Most Lambrettas have the fuse on the earth side. Probably because of the limited space available for mounting the battery, and it's proximity to the tank and toolbox should the retaining strap come off ?

I would Put it on the pos side.I would worry more about the ampage of the fuse.
Cheers
Stag

I also favour putting the fuse in the positive side for the same reason that Chris gave but I am willing to be convinced otherwise...so, what is the theory behind fusing the negative rather than the positive? (genuinely interested )

Colin

It was discussed in this thread some time ago......
viewtopic.php?f=10&t=2545&hilit=+fuse

As I said then, I always fuse the positive side, it's just my way of thinking. You can fuse both sides, many boilers and other machines do this in case of the supply being connected in the wrong polarity.
Belt and braces is fuse both. On my bike I made a rubber boot from an old bicycle inner tube to cover the positive terminal of the battery, this stops any grounded parts from touching the positive terminal.

I would go for the positive side.

Hi Raveydavy,
It is also useful to have a battery isolator switch (say on the dog leg that you can reach without taking panels off.)My lights, indicator and alarm have separate inline fuses mainly because I once had an intermittent fault that blew the fuse that turned out to be an internal short in the brake light switch where the 12volt contact inside the switch shorted on the metal switch plunger.
Grandpa

Neither, just one more thing to go wrong

Nelly wrote:It was discussed in this thread some time ago......
viewtopic.php?f=10&t=2545&hilit=+fuse

As I said then, I always fuse the positive side, it's just my way of thinking. You can fuse both sides, many boilers and other machines do this in case of the supply being connected in the wrong polarity.
Belt and braces is fuse both. On my bike I made a rubber boot from an old bicycle inner tube to cover the positive terminal of the battery, this stops any grounded parts from touching the positive terminal.

Thanks for the link, I can see the logic but a car battery would make an even bigger bang if the positive terminal was shorted to earth I do like your old inner tube idea though so will be copying that, might help keep the pesky spade terminals from falling off too

It's whichever you prefer, and if you look at an original 6v DC rectifier with the self contained fuse, then that's is actually fused on the Positive side of the battery.
But for me to better protect the battery from a short circuit I would fit the fuse to the earth side of the battery, wether it's a positive earth or a negative earth, simply because of the way the battery strap is fitted. If the strap comes loose and does touch the earth side of the battery it will not harm it but if it touches the feed side of the battery and short circuits it should blow the fuse instantly preventing the battery from being damaged or causing sparks near to the fuel tank and carb.

Cars seem to have very big batteries with hundreds of amps stored, so a fuse of that size is not likely to be fitted, instead it's most likely better to fit an earth strap and add many smaller fuses to the feed side from the battery and protect each individual circuit. Which seems to be how it's done.

For a 12v DC lambretta with a very small amperage battery fitted, I don't think there's really a wrong or right way, more just a preference.

Cheers chaps. I see the logic of fusing the earth side. Had never thought about the strap shorting across the terminals. However I'm looking at adding a 12v cigarette lighter and usb socket and want to protect the kit hanging off that. So Belt and braces approach makes sense, if not a bit more faff troubleshooting when it all stops.

I'm now wondering if there's more sensitivity to a short circuit or surge on either side.

Eden.. Why bigger on the earth side?

Grandpa, isolator switch sounds a bit too involved for the likes of me

Isolator switch is dead easy, it just turns the the connection between the battery and the loom on or off. It means that some funny tw@t can't work your horn or put a brick on your brake pedal and drain your battery. It can also prevent small earth leaks draining your battery when you're not using the scooter.

Anyone have a link for the best type of isolator switch to use , didn't want anything to bulky that could behind away
Merry Christmas all James

Hi Raveydavey.
As Ross states it is easy to fit an isolator switch.Instead of bolting your battery earth lead to frame you connect to earth via a switch (15amp toggle switch).Mount it on the rear near side dog leg, slide it inside a piece of cycle inner tube to give it some protection from elements.
Grandpa
pic added 16:54
Note flywheel cover has cloth over it as I keep dropping screws through the grill.also note earth point just above switch for wassell,braided earth from ht coil,engine and battery earth via switch

Cheers Grandpa and Ross. Can you please point me in the right direction to get hold of one of these?